#region Copyright (C) 2005 - 2008 Giacomo Stelluti Scala
//
// Command Line Library: OptionAttribute.cs
//
// Author:
//   Giacomo Stelluti Scala (giacomo.stelluti@gmail.com)
//
// Copyright (C) 2005 - 2008 Giacomo Stelluti Scala
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.
#endregion

namespace SMS.CommandLine
{
        using System;
        using System.Reflection;

        /// <summary>
        /// Indicates the instance method that must be invoked when it becomes necessary show your help screen.
        /// The method signature is an instance method with no parameters and <see cref="System.String"/>
        /// return value.
        /// </summary>
        [AttributeUsage(AttributeTargets.Method,
                AllowMultiple = false,
                Inherited = true)]
        public sealed class HelpOptionAttribute : BaseOptionAttribute
        {
                /// <summary>
                /// Initializes a new instance of the <see cref="SMS.CommandLine.HelpOptionAttribute"/> class.
                /// </summary>
                public HelpOptionAttribute()
                        : this(null, "help")
                {
                }

                /// <summary>
                /// Initializes a new instance of the <see cref="SMS.CommandLine.HelpOptionAttribute"/> class.
                /// Allows you to define short and long option names.
                /// </summary>
                /// <param name="shortName">The short name of the option or null if not used.</param>
                /// <param name="longName">The long name of the option or null if not used.</param>
                public HelpOptionAttribute(string shortName, string longName)
                {
                        this.ShortName = shortName;
                        this.LongName = longName;
                }

                /// <summary>
                /// Returns always false for this kind of option.
                /// This behaviour can't be changed by design; if you try set <see cref="SMS.CommandLine.HelpOptionAttribute.Required"/>
                /// an <see cref="System.InvalidOperationException"/> will be thrown.
                /// </summary>
                public override bool Required
                {
                        get { return false; }
                        set { throw new InvalidOperationException(); }
                }

                internal static void InvokeMethod(object target,
                        Pair<MethodInfo, HelpOptionAttribute> pair, out string text)
                {
                        text = null;

                        MethodInfo method = pair.Left;
                        if (!CheckMethodSignature(method))
                                throw new MemberAccessException();

                        text = (string)method.Invoke(target, null);
                }

                private static bool CheckMethodSignature(MethodInfo value)
                {
                        return value.ReturnType == typeof(string) && value.GetParameters().Length == 0;
                }

        }
}
